This invention is concerned with semiconductor manufacturing processes, and is more particularly concerned with apparatus and methods for controlling deposition chambers.
Semiconductor devices are made on substrates, such as silicon wafers or glass plates, for use in computers, monitors, and the like. These devices are made by a sequence of fabrication steps, such as thin film deposition, oxidation or nitration, etching, polishing, and thermal and lithographic processing.
Thin film deposition typically is performed in a low-pressure processing chamber. In chemical vapor deposition, a wafer or other substrate is loaded into a processing chamber and is exposed to a process gas under suitable conditions for deposition of the process gas or a component of the process gas in the form of a thin film on the wafer.
There are a number of different varieties of chemical vapor deposition processes, of which one of the more recently developed is referred to as atomic layer deposition (ALD) or atomic layer chemical vapor deposition (ALCVD). In atomic layer deposition, many thin film layers are deposited on the wafer in a repetitive process in which the wafer is alternately exposed to more than one process gas. Each cycle of an ALD process entails opening and closing a number of valves which control the flow to the processing chamber of process gases or a purge gas. Because each cycle is repeated numerous times, the amount of time required to generate, transmit and execute valve opening and closing commands may be a significant factor in the overall elapsed time required to complete an ALD process. The present inventors have recognized that a key to improving throughput for ALD processes lies in shortening the xe2x80x9crefresh timexe2x80x9d for valve control commands, where xe2x80x9crefresh timexe2x80x9d refers to the time required to generate, transmit and execute a command.
In accordance with the invention, there is provided a valve control system for a semiconductor processing chamber. The valve control system includes a system control computer and a plurality of electrically controlled valves associated with a processing chamber. The valve control system further includes a programmable logic controller in communication with the system control computer and operatively coupled to the electrically controlled valves. The programmable logic controller may control the electrically controlled valves with a refresh time of less than ten milliseconds, and preferably with a refresh time on the order of one millisecond (msec).
The valve control system may further include an interface board and a driver circuit coupling the programmable logic controller to the electrically controlled valves. The interface board may include solid state relays.
The programmable logic controller may include an output power supply adapted to provide an output signal from the programmable logic controller. The valve control system may further include an interlock circuit operatively coupled to the output power supply and adapted to disable the output power supply upon occurrence of an interlock condition.
The system control computer may be operatively coupled to the output power supply of the programmable logic controller and may be adapted to disable the output power supply in response to an operator input signal. The valve control system may include a control panel operatively connected to the system control computer and adapted to receive input from a human operator.
The plurality of electrically controlled valves of the valve control system may include a first valve, a second valve and a third valve. The first valve may be coupled to a source of a first process gas, the second valve may be coupled to a source of a second process gas, and the third valve may be coupled to a source of a purge gas.
According to another aspect of the invention, a method of operating a valve associated with a semiconductor processing chamber is provided. The method includes generating an operation command for the valve, transmitting the generated operation command to the valve, and executing the transmitted operation command at the valve. The generating, transmitting and executing steps may all be performed within a time period that does not exceed 10 msec.
According to still another aspect of the invention, a method of operating a valve associated with a semiconductor processing chamber is provided. The method includes providing an electrically-controlled valve and downloading a process recipe command from a system control computer to a programmable logic controller. The method further includes repeatedly generating open and close commands at the programmable logic controller in accordance with the downloaded process recipe command. Further included in the method are steps of transmitting the open and close commands from the programmable logic controller to the electrically-controlled valve, and repeatedly opening and closing the electrically-controlled valve in response to the transmitted open and close commands.
The method according to this aspect of the invention may further include flowing a process gas or a purge gas to the semiconductor processing chamber in response to the opening of the electrically-controlled valve.
With the valve control system arranged in accordance with the invention, commands to open or close valves for process gases or purge gas may be generated and executed with a refresh time on the order of one millisecond. With such a rapid refresh time, the many repetitive gas flow cycles required for ALD can be performed in an efficient manner, thereby increasing throughput.
Aspects of the invention also call for a hardware interlock operating through the output power supply of the programmable logic controller so that safety requirements are satisfied. Moreover, in accordance with an aspect of the invention, solid state relays are employed in interface circuitry which interconnects the PLC with the valves. The use of solid state relays allows the system to operate with a long life, notwithstanding the very numerous open-close cycles required for ALD processing.
Further features and advantages of the present invention will become more fully apparent from the following detailed description of a preferred embodiment, the appended claims and the accompanying drawings.